The present invention relates to shunts for lamps, particularly lamps arranged in an electrical series with other lamps to prevent all the lamps in the series from losing power when one lamp is removed from its socket.
Lamps such as those in decorative light strings are often arranged electrically in series. When thus arranged, the removal of one lamp will cause an open circuit and the entire series will lose electric power. In a set of Christmas lights on a Christmas tree, for example, it is a tedious task to find which socket is missing its bulb. Unless the empty socket is spotted by luck, one must begin at one end of the string and look at each socket in turn until all of the empty sockets are found.
There have been many attempts to produce shunts to keep power flowing to subsequent lamps in the light series when a lamp in the series burns out or is removed. Most of these involve a shunt wire, often with an oxide coating, or a solid state device, placed either in the lamp globe or in the socket such as a set of diodes that pass current to the next light when the filament burns out. Another approach involves use of a mechanical shunt in the socket to address the particular problem of loose or missing lamps. An example of such a shunt is found in U.S. Pat. No. 6,257,740, which is incorporated herein in its entirety by reference, and is issued to the present inventor and is commonly owned.
The device described in the '740 patent shows a pair of conductive spring terminals that are forced apart when the lamp and its base are inserted into the socket and spring together when the lamp and lamp base are withdrawn. This device works well but nonetheless there remains a need for other ways of shunting the current in a series light string.